1. Field of the Invention
The present invention relates in general to a method of and a device for measuring the radius of a rotating grinding wheel without stopping the wheel which is supported by at least one pivoting arm of predetermined length and urged against an object to be ground having predetermined dimensions.
This invention is applicable more particularly but not exclusively to the measurement of the radius of a grinding wheel in a machine for removing cracks from billets, or like machines.
In metallurgical processes, after a shaping or treatment operation, a metal product displays a given surface condition or appearance characterised by the distribution, shape, depth and amplitude of its irregularities, and also by its light-reflecting capacity, structural condition and physico-chemical and mechanical properties. Furthermore, in some instances surface defects such as cracks, scratches, inclusions, oxide layers, burrs, blisters, chinks, etc. . . are observed. A surface cleaning operation, notably for removing cracks on ingots and semiproducts such as blooms, slabs, billets, etc. of steel, notably hard steel or alloy steels, is performed as a rule by grinding. Now in this grinding operation it is necessary to constantly measure the diameter or radius of the grinding wheel, which varies with time due to normal wear, in order to control the rotational speed of the grinding wheel according to the unavoidable variation in the diameter or radius thereof, and thus keep the peripheral velocity of the grinding wheel at a substantially constant value.
2. Description of the Prior Art
It has been proposed to measure the diameter of a grinding wheel by means of a radio-active power source and of a probe associated with flicker meters or scintillation counters. A device of this known type operates as follows: the wheel acts as a screen between the source and the counters, so that the greater the wheel wear, the smaller the screen and the greater the amount of radiation picked up by the counters. Electronic means are thus enabled to deliver a voltage proportional to the diameter or radius of the grinding wheel. The order of magnitude of this voltage variation ranges from -3 V for a new grinding wheel to -10 V for a worn wheel. Nevertheless, this prior art arrangement is objectionable on account of the relatively long time period necessary for stabilizing the system (about 15 minutes), the poor stability of the output voltage, the poor resistance of the probe to shocks and vibration, and also the difficulties encountered in many countries for obtaining a proper certification of the source of radio-active power and the necessity of providing efficient safety means in case of faulty operation of one or several counters.